More smoke was blowing into Butte County Friday morning than over the previous few days, and air pollution levels were into the range of being unhealthy for some people.

The Butte County Air Quality Management District rated the air in Chico as unhealthy for sensitive groups — children, the elderly, and those with chronic lung or heart problems — and advised them to reduce heavy or prolonged exertion.

The problem isn’t the smoke you see, but the microscopic bits of soot and ash that can be inhaled deep into the lungs and cause health problems. It’s called particulate matter, and on Friday monitors in Chico and Paradise were recording an average higher than a federal level of concern.

The smoke was largely from the Ranch Fire burning in the Mendocino Forest, north of Clear Lake and into Glenn County. The fire was at 373,475 acres Friday, having grown almost 7,000 acres overnight, according to Cal Fire. It was 67 percent contained.

The fire was most active on its north and northeast flanks. Firefighters were conducting backburns to strengthen fire lines, which was contributing to the amount of smoke. There were 3,457 firefighters working the blaze.

Farther north, the Carr Fire West of Redding was 229,651 acres and 93 percent contained. The Redding Record Searchlight reported residents who had been evacuated had reported $118,713 worth of goods had been stolen from their empty homes, ranging from a gold bar to muffins.

Redding Police Chief Roger Moore said he expected that figure to rise.

The Hirz Fire on the McCloud River Arm of Lake Shasta was 22,047 acres and 17 percent contained.